An information of a revolution (a revolution speed, a number of revolutions per unit time, or simply referred to as a revolution number) of an essential part of a power plant such as an engine or a motor and a continuously variable transmission is needed for the control of the power plant and the continuously variable transmission. This revolution is detected by a revolution sensor and is utilized for the control.
For example, in a belt type continuously variable transmission connected to the power plant of an automotive vehicle, an input revolution sensor (a primary revolution sensor) detecting the revolution of a primary shaft and an output revolution sensor (a secondary revolution sensor) detecting the revolution of a secondary shaft are provided, a target gear (shift) ratio is calculated on a basis of an input information including the detection information from these revolution sensors, and a gear shift control is carried out in order for the gear (shift) ratio to become this target gear (shift) ratio.
However, in a case where an abnormality occurs in either or both of the input revolution sensor and the output revolution sensor, if the target gear (shift) ratio is calculated on the basis of the input information including the detection information from these revolution sensors, an appropriate target gear (shift) ratio cannot be obtained and an appropriate gear shift control cannot be achieved. Therefore, when a determination is made that the abnormality occurs in the revolution sensor(s), a fail-safe processing is carried out.
In addition, a lower limit secondary pulley pressure is calculated on a basis of the revolution speed of the primary shaft detected by the input revolution sensor. In a case where the secondary pulley pressure detected by the sensor is lower than the lower limit secondary pulley pressure, the determination is made that, in the primary pulley side, a slip occurs in the belt and a gear (shift) ratio fixture control is carried out.
Incidentally, as the revolution sensor, it is general that a digital encoder constituted by a sensing rotor (a signal rotor) installed on a rotary body such as the primary shaft or the secondary shaft and a sensor installed in a contactless manner against this sensing rotor. A plurality of teeth (projections) are installed on an outer peripheral surface of the sensing rotor. The sensor generates pulse signals corresponding to the teeth of the sensing rotor when the rotary body is revolved. The revolution speed of the rotary body can be obtained from this pulse signals and accompanied timer signals.
However, if the revolution state of the rotary body is tried to be grasped on the basis of the pulse signals, the pulse signals are outputted in response to a slight revolution of the rotary body. The pulse signals are outputted due to noises. In these cases, the revolution state of the rotary body is often erroneously grasped. If the revolution state is erroneously grasped, the control based on the revolution state cannot appropriately be carried out. In addition, an erroneous determination is made that the revolution sensor which is normal in nature has failed.
A technique which focuses on such a respect as described above is disclosed in a patent document 1. This technique is such that, in a case where a revolution pulse is generated by comparing a detection waveform detected by the sensor with a predetermined reference voltage, a switching element which electrically interrupts a high side of a detection element and a predetermined low voltage point of place is installed and, in a case where the revolution detection is not required, the switching element serves to inhibit the revolution detection. Thus, the revolution erroneous detection due to the noises or so forth can be prevented.
Incidentally, in a case where, in the automotive vehicle in which the above-described belt type continuously variable transmission is equipped, the abnormality of the input revolution speed and the slip of the belt are determined, a fail determination logic as will be described below is generally used.
In details, in a case of the determination of the belt slip, the determination is made that the belt slip occurs when, under a situation in which the vehicle is stopped and the primary shaft is stopped, a state in which revolution speed (a post processing revolution speed) Nf which is a filter process of the detection pulse data of the input revolution sensor exceeds a predetermined revolution speed NSL is continued for a time equal to or longer than a predetermined time TSL. In addition, for the determination that a line breakage of the input revolution sensor, the determination is made that the line breakage of the input revolution sensor occurs when no input of the pulse is decided after post processing revolution speed Nf exceeds another predetermined revolution speed NSN.
However, it is determined that, in such a general fail determination logic as described above, in the automotive vehicle in which the above-described belt type continuously variable transmission is equipped, a case occurs where the erroneous determination is made that the line breakage occurs in spite of the fact that the input revolution sensor is normal and a case occurs where the erroneous determination is made that the belt slip occurs in spite of the fact that no belt slip occurs. In each of the cases, it is determined that an abnormal input of the pulses of the revolution sensor is a cause.
When specifically considered, in a case where, with a clutch connecting the power plant with the continuously variable transmission separated, the power plant is driven, the input revolution sensor of the primary shaft is, sometimes, responded to output short period pulses although the primary shaft is, in nature, in the stopped state. In this case, an instantaneous revolution speed Nm of the primary shaft often becomes an extremely high revolution speed from the short period of the pulses. Thereafter, the pulses are not inputted from the input revolution sensor. However, a function which holds post processing revolution speed Nf, equipped in the vehicle, (a function which holds an immediately before revolution speed in a revolution pulse no input state of a tire lock) is operated to hold post processing revolution speed Nf of the primary shaft calculated immediately before until another predetermined time TWL (in general, TWL>TSL) has passed.
Consequently, when a state in which post processing revolution speed Nf caused by the above-described short period pulses exceeds predetermined revolution speed NSN is continued equal to or longer than predetermined time TSL, the determination is made that the belt slip occurs. In addition, there is a case where post processing revolution speed Nf caused by the above-described short period pulses exceeds predetermined revolution speed NSN. Hence, thereafter, when no input of the pulses is determined, the determination is made that the line breakage of the input revolution sensor occurs. Therefore, such erroneous determinations as described above are desired to be avoided.
In the technique described in patent document 1, the revolution detection is inhibited according to necessity. Hence, a condition setting to inhibit the revolution detection is not easy. In addition, when a hardware structure of the apparatus is added in such a way that the switching element is newly added, a rise of a cost will be introduced. Hence, while the rise of the cost is suppressed, the avoidance of the erroneous determinations is desired to be achieved.